Annunciator system



Oct. 15, 1963 A. F. sPERRY 3,107,349

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3,07,349 ANNUNCiATi- SYSTEM Albert F. Sperry, Evmston, El., assigner, by messie assignments, to The Scam instrument Corporation, a corporation of Elinois Filed ct. lo, 1955, Ser. No. 757,72@ 6 Claims. (Ell. 34h-M3) This invention relates to annunciator systems of the type wherein a visual alarm unit, such as a light, is provided for each variable to be monitored, and, when a variable becomes abnormal, va corresponding pair of signal contacts controlled -by the variable are actuated to operate the corresponding visual alarm unit. Simultaneously with the operation of the visual alarm, an taudible alarm is sounded to attract the operators attention to a central control panel containing the visual alarm units associated with practically all the variables to be monitored in the plant involved, so that the operator can determine at a glance the condition of these variables. A manually operable aclmowledgement switch is usudly provided, which, when operated, at least silences the audible alarm, `and in some cases, changes lthe visual indicator of the visual alarm associated with the variable which just became abnormal.

Obviously, it is of utmost importance that annunciator systems be extremely reliable, since, otherwise, they could not fulfill their intended purpose. The problem :of reliability becomes of utmost importance especially in installations where the presence of an abnormal variable may create a situation which is dangerous to human life and safety, or where extremely expensive equipment is being mom'tored. it is a primary object of the present invention -to provide `an annunciator system having `features which greatly increase the reliability thereof over alarm systems heretofore utilized.

Another one `of the objects of the present invention is to provide such a reliable annuncia-tor system operating substantially exclusively with static control elements, such as transistors or cores and the like, preferably transistors, instead of with control elements having movable parts suc-h as relays, and furthermore, wherein the annunciator is most preferably constructed for utmost ilem'bility in operation, providing, for example, for operation with normally-open or normally-closed field contacts.

A still further `object of the present invention is to provide an annunciator system as above described wherein the circuit in which the signal contacts are located is '-a low energy circuit which will not sustain an arc or produce ignition in explosive atmospheres.

it has been common practice in annunciator systems to utilize common control elements in both the energization circuit for the visual and audible alarm units, so that failure of a control element in common with both of these units results in failure of the entire annunciator system. In accordance with one aspect of the present invention, the reliability of the annunciator system is substantially increased over these prior systems by operating the visual and audible alarm units respectfully through independent control circuits. For example, the control elements, such as relays, cores and transistors used in the visual alarm or audible `alarm control circuits, transistors being preferred, perform functions in only their own control circuits, so that failure of any one of the circuits to operate due to va defect therein will not affect the operation of the other con- .trol circuit. Thus, for example, if the control elements associated with a visu-al alarm light should become defective, the audible alarm units will operate when the variable with which the defective control element is associated goes abnormal. The sounding of the audible liillg Patented @et l5, 1953 alarm will attract the operators attention to the control panel containing the alarm lights of all of the variables. A test circuit is provided which simultaneously actuates all of the control circuits of the entire system, so that the abnormal variable can be determined by noting which alarm light remains unlighted.

As an additional feature of the invention, `at least two visual alarm lights are used per variable and each visual alarm light is placed in a separate control circuit wherein the defective operation of any control element in one of these control circuits will not effect the operation of the visual Ialarm light associated with the other control circuit. There are, thus, in the preferred form of the invention, three independent control circuits associated with each variable, with preferably no common circuit components except for the associated signal contacts, which control circuits respectively operate the audible alarm and `the two visual alarm lights. Thus, failure of any l or 2 circuits will still result in an alarm lwhen the associated variable goes abnormal.

in one very useful form of .the invention, the visual light indication of one of the alarm lights is a flashing indication which would attract the operators attention even if the control circuit associated with :the audible Ialarm would become inoperative. The other visual alarm iight may be operated directly from the signal contacts to provide Va steady-on light indication as long as the variable is normal. The control circuit which operates the latter alarm light is thus the most reliable circuit of lall since the only control elements therein are the condition-responsive signal contacts. The signal confacts, however, carry relatively large energizing current for the associated alarm light and thus sparking at the signal contacts is likely which would be undesirable in explosive atmospheres unless specially designed land costly signal contacts are used. In explosive atmospheres, therefore, it is preferred that all of the control circuits include control elements, preferably transistor gate 'and power amplifier units, whose inputs are controlled by low current control paths in which the signal contacts are located.

in the case where one of the visual alarm lights has a flashing indication, this visual alarm light together with the other visual alarm light having only a steady-on light indication can be placed behind a common translucent panel to simulate a single light source. rIlhe visual alarm light wmch provides a flashing indication can be operted by a bistable unit which is set in one condition by operation of the signal contacts to operate the light When the variable becomes abnormal and which is set to another condition to turn the light olf by momentarily operation of an acknowledgement switch. The other alarm light remains on as long as the variable remains abnormal. The overall light indication in this case is a flashing light for lan initial alarm, a steady light for an acknowledged alarm and no light for normal operation.

The audible alarm unit is also preferably controlled by a bistable unit which is set into one condition by operation of the signal contacts to Vsound the audible alarm Iand 'which is reset to its other condition by operation of the acknowledgement switch which turns the audible alarm off.

The above-mentioned bistable circuits most preferably include a pair of static control elements, transistors being preferred, and the bistable circuits control gate and power amplifier stages also preferably being transistors. Transistors are preferred over cores because the former operate from simple direct current power supplies whereas the latter require expensive, relatively high frequency power supplies where the cores are desirably small, inexpensive units. The bistable units of both the alarm light and audible alarm control circuits are set into their alarm initiating conditions by separate capacitor-resistor pulseorming networks connected to the direct current power supply through the signal contacts. When a pair of signal contacts operate to couple the inputs of the associated pulse-forming networks to one of the terminals of the power supply, a pulse is generated in the output of each pulse-forming network lwhich sets the associated bistable circuits.

As will appear, the most preferred embodiment of the present invention is designed for utmost exibility so that it can provide a number of modes of operation by simply changing the position of the Wipers of switches or jumpers or by removing a control element from or inserting the same into a plug-in socket or the like. In this way, the system can be made operable with normally-open or normally-closed signal contacts or with one or two alarm lights. The use of separate control circuits for the alarm lights enables the latter change to be made by simply adding a light and the necessary control elements mounted, for example, on a single plug-in unit.

Other objects, advantages and features of the invention will become apparent upon making reference to the specification to follow, the claims and the drawings Where- FIG. 1 is a diagram of an annunciator system, partly in box form, illustrating one of the simplest forms of the present invention using only one alarm light which remains on as long as the variable remains abnormal;

FIG. 2 is a modiiied form, partly in box form, illustrating a modification of the annunciator system shown in FIG. 1;

FIG. 3 is a still further improved form of the present invention wherein two alarm lights are used to provide an initial alarm and acknowledged light indication;

FIG. 4 is a chart illustrating the sequence of operation of the lights and the horn in the annunciator of FIG. 3 for various modes of operation thereof;

FIG. 5 is a further modification of the invention; and

FIGS. 6a and 6b is in a detailed circuit diagram of one exemplary form of the annunciator system illustrated in FIG. 3.

EMBODIMENT OF FIG. 1

In the'annunciator system shown in FIG. 1, a number of identical annunciator units are shown enclosed by dotted lines 2 which respectively represent those circuit components used exclusively with the individual variables to be monitored. Each of these annunciator units illustrated includes a visual alarm light 4 which may be an incandescant lamp .which is lighted in a steady-on condition when the associated variable is abnormal, and which is ot when the associated variable has returned to normal. A common audible alarm or horn 6 is used with all of the alarm units 2 and is sounded when any variable goes abnormal to attract an operators attention to a control panel (not shown) mounting all of the alarm lights 4, so the operator can tell immediately what particular variable has gone abnormal. A manually operable acknowledgement push button 8 is preferably provided, which, when depressed momentarily, silences the audible alarm 6. This simple type of'annunciator system is useful primarily Where it is unlikely that more than one alarm point will remain abnormal at any one time, since the annunciator system does not distinguish between the variable which has just become abnormal and one which is `still abnormal butV initially became abnormal some time before. Thus far, the annunciator system describedris an old and well known form of annunciator system. The aspect of the invention illustrated in FIG. 1 revolves around the provision of completely independent control circuits for operating both the various visual alarm lights 4 and the audible alarm unit or horn 6. Heretofore, the control elements which controlled the alarm light 4 also, in part, controlled the audible alarm 6, so that a defect in the operation of the basic control circuit would render the entire system inoperative.

The primary control for each annunciator unit 2 is an individual set of signal contacts ill or 10' controlled by the variable involved. The reference numeral lt) identies a set of normally-open signal contacts 10 shown in solid lines which are open when the associated variable is normal and which are closed when the variable is abnormal. A set of normally-closed signal contacts 10 is shown in dotted lines since they are used alternatively with the contacts 16. These are opened when the associated variable goes abnormal.

The normally-open set of contacts l0 are connected across terminals 12-12 which may be screw terminals, and when the normally-closed ield contacts lil are used, they are connected across a set of terminals 14-14, which may also be screw terminals. In the illustrated embodiment, terminals 12--12 are connected in series with a power bus 16 connected to the negative terminal of a source of direct current potential 18 which, for example, may be a 24 volt supply. The upper terminal 12 remote from the bus 16 is connected to a switch or jumper terminal 13.

The positive terminal of the D.C. supply 18 is shown connected to a grounded bus 18. The bus 18 is connected via a conductor 19 to one side of a normally-closed pushbutton test switch 20, and the other side of the test switch is connected to a N C. test bus 2i. The terminals 14--14 across which the normally-closed eld contacts itl' are connected are between NC. test bus 21 and a switch or jumper terminal 22. A current-limiting resistor 23 is connected between the switch or jumper terminal 22 and the power bus 16.

The uppermost terminal 12 remote from the lower power bus 16 is connectable to a common switch or jumper terminal 25 through the aforesaid switch or jumper terminal 13 and a switch wiper or jumper 26 during operation with normally-open signal contacts 1t?. The terminal 14 remote from the grounded bus 18 is connected to the common switch or jumper terminal through the aforesaid switch or jumper terminal 22 and the switch wiper or jumper terminal during operation with normallyclosed signal contacts. It should be apparent that the potential of the common switch point 25 will be at the potential of the power bus 16 when the set of normallyopen signal contacts l@ connected across the terminals 12-l2 are closed or the normally-closed set of signal contacts 10 connected across the terminals iid-14 are open.

Two completely independent control circuits extend from the common switching point Z5 which circuits respectively control the operation of the alarm light 4 and the horn 6. The control circuit illustrated for the alarm light 4 is the simplest circuit possible wherein the alarm light 4 is connected directly between the common switching point 25 and the grounded bus 18. Thus, when normally-open signal contacts are utilized, and the terminals 13 and 25 are accordingly connected together, closure of the signal contacts will apply the potential between the buses 18 and 16 to light the alarm light 4. On the other hand, during the operation of the circuit with normallyclosed signal contacts, where the terminals 22 and 25 are connected together, opening of the normally-closed signal contacts 10 places the alarm light 4 in series between current-limiting resistor 23 and power bus 18. When the signal contacts 1G are closed, the contacts shunt the alarm light 4. Resistor Z3 is necessary to prevent a short circuit between the buses I6 and 18 when the signal contacts 1G are closed. Its Value should be such that suliicient current passes through the alarm light 4 when the signal contacts lil are open to light the same brightly. f

The control circuit for controlling the horn 6 also extends from the common switching point 25 in parallel with the light 4, so that burning out of the light willy not affect the operation of the horn control circuit and, conversely, defective operation of the control circuiti for the horn 6 will not affect the operation of the light 4. This greatly increases the reliability of the annunciator circuit as compared to a system where common control elements are used for the horn and light 4 other than the signal contacts.

The hom control circuit includes a pulse-forming network or circuit 39 whose input extends from the switching terminal 25 of each of the control units 2 and whose output is connected to a horn bus 32. The pulse forming network 38 is a capacitor-resistor dilerentiating circuit which produces a pulse from a change in potential and preferably include means which passes only pulses having the polarity of the power bus 16, which, in lthe illustrated embodiment, is a negative voltage. The output of the pulse-forming network 3i) extends to one of the inputs of a suitable bistable unit 34 which may take a number of forms, and preferably includes a pair of static control elements, most desirably transistors. A bistable unit usually comprises two current-control elements capable of producing two different output states represented respectively in PIG. l by the shadedrand blank areas of box 34. An output line 36 extends from the bistable unit 34 to the input of a control stage 38 identified as a gate circuit 38.' vIt is possible that the bistable circuit 34 may itself also form a gate circuit, as found in many core bistable circuits, so that a separate gate circuit can be omitted entirely. The bistable circuit 34 in one yof its conditions of operation opens the gate 3S to enable power to pass to the input of another control element di) which is illustrated as being -a magnetic amplifier. When power is applied to the input of the magnetic amplifier 4G, energizing current from a 60 cycle commercial power supply 42 is caused to flow in the output thereof which current passes through horn 6 to energize the same.

Means are provided for resetting the bistable unit 343', such means including the previously mentioned acknowledgement pushbutton switch 8 connected between the power bus i6 and a second input to the bistable unit 34. Thus, momentary depression of the acknowledgement switch S will reset the bistable 34. This, in turn, de-energizes the output of the magnetic ampliier 40 to silence the horn 6.

To provide a common means for triggering all control circuits at once for test purposes when operating with normally-open signal contacts, an N.0. test bus `44 is provided. A rectifier 46 polarized to pass -the potential of bus i6 is connected between the N O. test bus 44 and the switch or jumper terminal 13 associated the normally-open contacts of each annunciator unit 2. The N.O. test bus is connected to the power bus 16 'through a normally-open 'pushbutton switch 4S. Closure of switch d8 feeds the voltage of power bus i6 to the pulseforming networks 3i) and the alarm lights 4 of all annunciator units 2, as does the closure of all the signal contacts 1t?. Where normally-closed signal contacts are used, opening of normally-closed pushbutton switch 2@ breaks the shunt circuit around alarm lights 4 to etect the coupling of the potential of power bus i6 to all the pulse-forming networks 3@ and the alarm lights 4 as does the opening of all normally-closed lsignal contacts 1G.

One of the drawbacks of the circuit shown in FIG. 1 lies in the arrangement for operation of the circuit with normally-closed signal contacts lli. The resistor 23 must be of sufficiently small value to enable the alarm light to be lighted brightly. Appreciably current may thereby flow through resistor 23 when signal contacts 10 are closed, resulting m appreciable power dissipation and heating of resistor Z2 which, in some instances, may be undesirable. The circuit of FlG. 2 overcomes this disadvantage and has other advantages as well, as will appear from the description to follow.

EMBODIMENT OF PIG. 2

The annunciator shown in FIG. 2 is similar to that shown in iFIG. l and common components have been 6. similarly numbered. The difference between the circuit of FlG. 11 and that of HG. 2 lies only in the control circuit for the alarm light 4. Instead of operating the alarm lamp 4 directly from the eld contacts, the light 4 is controlled by the output of a control stage generally indicated by reference numeral lSti. In the embodiment illustrated, the control stage 50 is a gate and power ampliier stage having an input line '56a and a pair of output lines 52-52. The gate and power amplifier stage 50 is set by operation of the signal contacts l0 or 10 to provide ilow of energizing current in the output lines 52-52. Line 52 is connected to power bus 18 and line 5-2 is connected to one of the terminals of alarm light 4, the other terminal of alarm light being connected to power bus 16. A dimming resistor 53 extends between line 52 4to the power bus 1S so that light 4 will be dimly lit when the associated variable is normal. A constant check on the operating condition of the light 4 is thus available.

The input line 50a to lthe gate and power stage is connected to the aforesaid common switching point or terminal 25 and the associated switchingterminals 13 and 22, are wired in the same manner shown in FlG. -1. The gate and power stage 5t) is -designed so that little or no current ow in the output lines 52-52 when the input line `Stir/z is effectively decoupled from the potential of power bus 16 and energizing current ows in lines 52-52 when the input line is coupled to the potential or" power bus l16. Accordingly, energizing current ows through alarm light 4 when normally-open contacts y10 close or normally-closed contacts lil open.

In the circuit of FlG. 2, the input line Stia -to the gate and power stage 50 can be fed from a low current (energy) circuit and, accordingly, the current-limiting resistor 23 maybe a large resistor relative to the value of fthe resistor 23 in the circuit of FIG. l which had to be suiiiciently small to enable the alarm light 4 in series with it to be lighted brightly. The resistor 23' accordingly has only a small amount of power dissipated in it. The use of a low energy input circuit has the further advantage that it enables the use of relatively inexpensive signal contacts l0 and 10 when used in explosive atmospheres because these contacts need not be designed to avoid the possibility of dangerous arcing. Low energy circuits will not sustain an arc which produces ignition in explosive atmospheres.

The circuits for controlling the bistable units 34 including the circuits in which the various pushbutton switches y8, 2t) and 43 are located are also low energy circuits.

The arrangement of the circuits shown in FIGS. l and 2 enables ready expansion thereoi` to include a second alarm light so Ithat the visual announcement of the annunciator -system may include visual indications for both initial alarm and acknowledge alarm conditions. in the embodiments of FIGS. 1 and 2, the acknowledged state of operation of the system is determined solely by -the existence `of 'an alarm light and the absence of the sound of the horn 6. As previously indicated, this type of system is practical primarily only in systems where, as a general rule, only one variable is abnormal at any one time. When a number yof variables are expected to be abnormal at the same time, it is desirable to be able to tell visually the difference between a variable which has just become abnormal and one which had become abnormal sometime before. The circuit of FIG. 3 is just such a circuit, and those elements shown in FIG. 3 which are also present in the embodiments of FIGS. l or 2 are identied by the same numberr The difference between the embodiment of FIG. 3 and that of FIG. 2 is thus the addition of a second alarm light 4 which may be, made to Hash .or have a steady-on condition when the associated variable initially becomes abnormal. Upon momentary depression of the acknowledgement switch 8, the light 4' may be turned off leaving only the alarm light 44 lit to indicate an acknowledged condition of the variable. That is, when both lights 4 and 4' are lit, this represents an initial lalarm condition of the Variable, and when only the light 4 is lit, this represents an acknowledged condition of the variable. When the light 4' gives a flashing indication, the lamps 4 and 4' may be mounted behind a common translucent panel 54 to simulate 1a single light presenting a dashing sequence commonly used in the annunciator iield, which comprises an overall flashing indication for =an initial alarm indication and an overall steady-on indication for an acknowledged alarm condition.

IThe control circuit for operating the second control light f4' includes a pulse-forming network 64 similar to the pulse-forming network `30 and whose input is connected in parallel with the input of Ithe pulse-forming network 30. The output of the pulse-forming network 64 extends to one of the inputs of a bistable unit 66, which may be similar to the horn bistable unit 34. As in the latter bistable, the bistable unit 66 may include two current control devices, preferably transistors, adapted to have opposite output states represented respectively by the shaded and blank areas in the box 66. The pulseforming network 64 produces a negative pulse in response to the connection of the input line to the power bus 16 and this pulse sets the bistable 66 in a condition where a gate-opening voltage `appears in an output line 68 thereof. The output line 68 extends -to the input 70a of an and gate and power amplifier stage 7G. The and gate and power amplifier stage 7G has a second input 7Gb connected to a common switching terminal 73 which may be selectively connected through a switch wiper or jumper 74 to a terminal 76 leading -to a flasher bus 78 or to a terminals() leading to the power bus 16. When thecommon switching terminal 73 is connected to Ithe asher bus, a voltage alternating at a Visible flashing rate between a value which will be referred to as a gate-opening voltage and a gate-closing voltage is connected to the input line 70h. A suitable asher unit -S-l connected between the asher bus 78 and the power bus 16 provides this alternating voltage. The iiasher 81 is preferably one which is made entirely of static components, such as transistors, Ialthough, in accordance with the broadest aspect of the invention, it could be a cam-operated mechanical switch which is alternately opened and closed to couple and uncouple the potential of power bus 16, which would be said gate-opening voltage. The and gate and power stage 70 is ydesigned so that appreciable current iiows in a pair of output lines 7.1 and 71' when a gate opening voltage is supplied simultaneously to both the inputs 76a and 7tlb. `Output line -71 is connected to power bus 1S and output line 71 is connected to one terminal of alarm light `4', :the opposite terminal of alarm light 4 being connected to power bus 16. A dimming resistor 72 extends from said one terminal of the alarm light 4 to the power bus 18. yIt is thus apparent that when the bis-table unit 66 is set by the output pulse generated by pulse-forming network 64 upon operation of signal contacts and .10', the resultant gate-opening voltage appearing on output line 61SA will, in association with the alternating voltage at input 7tlb of gate 70, cause the alarm light 4' to iiash brightly on and ott.

It a non-hashing alarm indication is desired, common switching terminal 7-3 is connected to the power bus -16 through the switch wiper or jumper 74 and a terminal 8i?. In such case, the alarm lights v4 and 4 would be mounted to display their indications separately. Since input 7Gb is always connected to the gate-opening potential of power bus 1S, the setting of the bistable 66 upon operation of thesignal contacts will result in a steady-on condition of alarm light4.

Acknowledgement of the annunciator system is ob- 'tained through a circuit including an acknowledgement bus 82 extending from .the normally-open pushbutton acknowledgement switch 8, in turn connected to the power bus 16.V The acknowledgement bus 82 is connected to the bistable units 66 of each annunicator unit 2 through a branch line 83 connected to an auto reset switch or jumper terminal 86 lwhich may be connected through a switch wiper or jumper 8S to la common switching terminal 9G connected to a second input 84 of the associated bistable unit `65. With the switch wiper or jumper 88 in the position just described, momentary closure of the acknowledgement pushbutton switch `S will couple a reset voltage to the bistable unit 66 which resets the bistable unit to terminate the gate-opening voltage on the output line 68 thereof. This deenergizes the output of the and gate and power amplifier 79 to effectively deenergize the second alarm light 4. Due to the permanent connection of the dimming resistor 72, the so-called de-energized condition of the alarm light is a dimly lit condition. The acknowledged state of the annunciator involved is then the lenergized condition of the light 4, should the variable still be abnormal. :f the variable returns to normal, and the normally-open signal contacts 1G accordingly open or the normally-closed signal contacts 10 accordingly close, then the alarm light 4 will be deenergized which, in ythe case being illustrated, is a dimly lit condition.

lIn the embodiment of FIG. 3, means are provided for selectively providing for a lock-in or a non-lock-in operation of the annunciator. By non-lock-in is meant that a visual alarm indication on the alarm lights will be displayed only when the variable is abnormal. Lock-in operation, on the other hand, is where momentary alarm conditions are visually indicated at least until acknowledgement. This means may include a bias line or the like 93 associated with each bistable unit 66 which inhibits or cancels a set condition of the bistable funit when it is disconnected from the potential of power bus 16 and allows or maintains a set condition thereof when coupled to the potential of :the power bus '16. The bias line `93a extends to a common switch or jumper terminal `95 which may be connected through a switch wiper or jumper 97 to a switch or jumper terminal 99, in turn, connected to the common switching terminal 25 leading to the signal contacts 10 or 10', or to a switch or jumper terminal 161 which may be connected through a resistor 103 to the power bus 16. When the bias line 93 is connected to the nonlock-in terminal 99, the bistable unit 66 can be set when the normally-open signal contacts 10 close or the normally-closed signal contacts open since then the bias line 93 is coupled to the potential of the power bus. Upon return of the signal contacts to their normal indicating positions, that is, upon opening of the normallyopen signal contacts d0 or closure of the normally-closed contacts V1G", the bias line ll() will be decoupled from the potential of power bus 16 to cancel the set condition of Vthe bistable funit. When the bias line 93v is connected to the lock-in terminal 101, it is permanently connected to the power bus :1r-6, so that the bistable unit maintains its set condition independently of the position of the signal contacts until externally reset.

For non-lock-in operation, the horn will sound even for momentary alarms, and the horn is silenced by depression of the acknowledgement switch. IFor lock-in operation with the circuit being described, it is desirable to separate acknowledgement of the horn from acknowledgement or reset of the alarm lights. To this end a reset bus y107 is provided which is connectedtto each annuciator unit 2 by a conductor i198 to a manual reset jumper terminal 169 with which the switch wiper or jumper 88 may be connected to interconnect the reset input line 484 -wi-th the reset bus 107. A normally-open reset switch 110 is inserted between the bus 107 and the power bus 16. Thus, for manual reset operation, momentary depressions of the acknowledgement switch 3 will not eiect the condition of the bistable unit 66, but will merely silence the horn6 in the manner previously explained in connection with the circuit of FIG.

1. Momentary depression of the reset switch 211%) will Y reset bistable unit 66 and turn olf the alarm light 4.Y

age pulse is thus generated across resistor 131 during the charge of capacitor 129, which voltage is `coupled ythrough the rectier 137 and resistor 135 to the horn bus 32 which sets the horn bistable to be described more fully hereinafter.

The pulse-forming network 64 associated with the bistable uni-t 66 which controls the operation of the second alarm light 4 is comprised of capacitor and resistor elements which correspond to the resistor and capacitor elements just described in connection with the pulseforming network 3G. The corresponding elements have been similarly numbered, except that a prime has been placed on the numbers of the corresponding elements of the pulse-forming network 64 because, depending upon the circuit conditions of the various bistable circuits associated respectively with these pulse-forming networks, the values might -be somewhat diiferent. Such considerations, for example, Iare the reason for the addition of a pair of resistors 139 and 141, the resistor 139 extending between the resistor 131' and the plus 12 volt power bus 118 and the resistor 141 extending between the juncture of resistors 121 and 139 and the grounded side of the resistor 127. Since the actual details `of the pulse-forming networks 3G and 64 form no part of the present invention and may take a number of forms, the actual values of ythe various elements need not be given. The pulsefonning network 64 has an input line 142 and an output line 143 upon which a negative pulse of proper magnitude is generated therein to set the following bistable unit 66 when the input line 142 is connected to the potential of the negative 24 voltage power bus 16.

Bistable Unit 66 Y Bistable circuit 66 may take a variety of forms. In its less preferred form, it could include a pair of 'currentcontrol devices wherein one of the current-control devices operates at any given time in a relatively high current conducting condition while the other control device operates in la relatively low or no current conducting condition. 'I'his type of bistable circuit has certain disadvantages when the bistable circuit is incorporated in an annunciator circuit where the system `operates in one state, that is, in a normal indicating state practically all of the time, and only infrequently needs to operate in an alarm indicating condition. It would, for example, be desirable if the current-control devices or" each bistable unit ordinarily operates in a low or no current conducting condition, particulanly in the case where the current control devices are transistors, since transistors will last a much Ilonger period of time and operate more reliably if they are both normally non-conducting. To this end, the bistable circuit 66' is provided with a pair of transistor current control devices 145 and 147 which, in .thenormal condition of the bistable, are both in ia low-current conducting state, and, in the other condition of operation thereof are both in a high-current conducting state. Another advantage characteristic of this type of bistable unit where both are conducting or non-conducting is that the circuit `operates more consistently and reliably. It the bistable circuit is one where one of the transistors is in a highly conductive state while the other transistor in a low conductive state, racing is possible so that it is diicult to obtain initial conduction of the same transistor each time the energizing potential is fed to the transistor. Even where a given bistable unit is consistent in its operation, inherent differences in the char- Y acteristics of transistors of the same type might change the initial operating condition thereof in another similar unit.

The bistable circuit `66 includes an NPN type transistor 145 having base, emitter and collector electrodes 145:1, 145b and 145C, respectively; The other transistor 147 is va PNP type transistor having base, emitter and collector electrodes 147:1, 147]) iand 147C, respectively. The base electrode 14551 of transistor 145 is connected to the juncture of resistors 150 and 152, the resistor 156 being 12 connected 4to the plus 12 volt power bus 118 and the resistor 152 being connected through a resistor 154 to the negative 24 volt power bus 16.

The base electrode 14701 of the transistor 147 is connected through series connected resistors 156 and 153 to Ithe plus 12 volt power'bus 118. The base electrode 147:: of .the transistor 147 is also connected to the aforementioned bias line 93 extending to the common switching terminal 95. As previously explained, when lock-in operation is desired, the bias line 93 is connected always to the power bus 16. In such case, the switch wiper or jumper 97 would be connected to the switch terminal, 161. Due to the specific bistable circuit disclosed in FIG. 6a, the terminal 101 is connected through a resistor 1113 to the power bus 16 rather than being `directly connected thereto.

Also due to the particular circuitry illustrated in FIG. 6:1, two switch or jumper terminals 99 and 99' are shown, rather than a single terminal 99, for providing non-lockin operation. The switch wiper or jumper 97 interconnects terminals and 99 for non-lock-in operation when normally-open signal contacts 10 are utilized. Terminal 95 is connected by switch wiper or jumper 97 to the terminal 99 for non-lock-in operation when normallyclosed signal contacts 10 are utilized. The separate contacts 99 and 99 are used in order to insert diierent resistors 161 and 163 in the circuit respectively when normally-open and normally-closed signal contacts are used, since the circuit associated with the two types of signal contacts is somewhat ydifferent as has been explained. Resistors 161 and 163 are both connected -to the common switching terminal 25. The actual values of the various resistors associated with the bistable circuit will not here be given since the present invention does not depend upon such Values and lthe precise values to be used in any given instance depends upon various factors which are uirnportant insofar as this disclosure is concerned.

To continue the description of the bistable unit 66, the emitter electrode b of the transistor 145 is connected the emitter electrode 147b of transistor 147. T-he juncture of the emitter electrodes 145b and 147b is connected by a conductor 166 to the grounded bus 1S.

The collector electrode 145C of transistor 145 is connected by a conductor `152 to the juncture between resis; tors 156 and 158. The output line 68 of the bistable unit 66 'also connects to this point, and, as will appear, the potential on the output line l68 is made substantially the potential of the plus 12 volt power bus 118 when the variable involved is normal, and, to this end, the resistor 158 is made substantially less than the sum .of the values of resistor 156 and the other resistors in series therewith. When the variable is abnormal, the potential at the output line 68 is substantially the potential of the ground bus 1S. The emitter electrode 147C of the transistor 147 is connected to the juncture between resistors 152 and 154.

When the normally-open signal contacts 10 rare open or the normally-closed signal contacts 19 are closed for non-lock-in operation of the annunciaton the bias line 93 of the bistable circuit has a potenti-al applied thereto which maintains the transistor 147 in a non-conductiveV output state. The potential of the base electrode ot the PNP transistor 147 would'therefore have to be positive relative to its grounded emitter electrode 147b. For normally-open signal contacts the bias circuit for the base eiectrode 147:1 extends only to the positive bus 11S through resistors 156' and 158. Por normally-closed signal contacts, the bias `circuit can be traced from ground bus 18 through conductor 19, bus 21, signal contacts 10', terminals 22 and 25, resistor 161, 1terminals 99 and 95 and resistors 156 and 158 leading to the positive bus 11S. The potential of the base electrode 147:1 is therefore positive in either case. The potential at the base electrode 145:: of transistor 145 is also such that the latter electrode has a negative potential with respect to ground 13 which ensures a non-conductive `state of the NPN type transistor 14S. To this end, lthe ratio of the sum of the resistance values of resistors 152 :and 154 on the one hand to the resistance value of resistor 159 is such that this negative potential prevails.

Closure of the normally-open signal contacts or opening of the normally-closed signal contacts 16" also forms a bias circuit which, in the absence of other signal voltages would place a positive potential on the base electrode 147a. This bias circuit can be traced from the negative bus 16 through resistor 23 for NC. operation or signal contacts 1G for N.O. operation to the common switching terminal 25, then through resistor 163 or 161 and resistors 156 and 158 to the positive bus 118. However, operation of the signal contacts 1i)` yor 1li' also causes a negative pulse to appear at the output of pulseforming network 64 which pulse is coupled directly to the base electrode 147a to, momentarily at least, start the transistor 147 conducting heavily. Since the resistance between the emitter and collector electrodes 14711 and 147C may be considered negligible during the high conductive state of the transistor 147, the ground potential of the emitter electrode 1i7b is connected to the point at the top of the resistor 154. When ground is applied to the latter point, a positive potential is applied to the base electrode or" NFN transistor 14S which starts this transistor conducting. This applies the ground potential of the emitter electrode 145i; to the output line 68 and the bottom of resistor S. This obviously will place the bottom end of resistor 156 connected to base electrode 147e: at a negative potential which maintains the PNP transistor in its highly conductive state. The feedback circuit just described enables the triggering of the bistable circuit into a condition Where both transistors are simultaneously in a highly conductive state upon the application of a negative pulse to the base electrode E1l-7a of the lower transistor 142-7.

The bistable unit 66 can be reset into its condition where both transistors are in a relatively non-conductive state in two ways. When the circuit is arranged for ncn-lock-in operation, re-opening of the normally-open signal contacts 19 or re-closure of the normally-closed signal contacts 1G re-establishes the normal bias circuit above described which renders the lower transistor 147 non-conductive. As soon as this transistor becomes nonconductive, the potential at the upper end of resistor 154 which had maintained the conductive state or" the upper transistor 145, disappears, thereby enabling the normal bias voltage drop across the resistors 15b, 152 and 154 to render the upper transistor non-conductive.

VThe bistable unit can also be rendered substantiall non-conductive upon application of a negative pulse to the base electrode 145e of the upper transistor 1415. Thus, when the reset pushbutton 16% is momentarily closed, a negative voltage appears on the reset bus which is coupled through a resistor 1&9" and a properly polarized rectifier 171 to the base electrode dt-5o. This momentarily renders the transistor 15.15 non-conductive. This removes ground potential from the bottom of the resistor 15S which had previously maintained the lower transistor 15H7 conductive. This, then, re-establishes the above-mentioned bias circuit. The return of the signal contacts to their normal condition indicating position does not result in any pulse at the outputs of pulseforming networks 3@ and 64 due to the discharge of capacitors 129 and 129 because the pulse generated within each oi these networks is positive and the associated rectitiers 137 or 137 do not pass positive pulses.

When the transistors 145 and 147 are in their relatively high conductive states, as above indicated, the potential on the output line is substantiallyground potential. When, on the other hand, the transistors iare relatively non-conductive, the potential at the output line 63 is effectively the potential of the positive l2 volt power bus 113 due to the fact that resistor 1g?) is substantially smaller than the sum of the resistance of the resistors between the bottom of resistor y15% and the negative power bus 16.

And Gate and Power Amplier 70 ln the preferred embodiment of the invention being illustrated, the and gate and power amplifier 70 inclu-des a transistor control element 173` having base, emitter and collector electrodes 173e, 173!) and 173C, respectively. The transistor 173 is connected as a twoinput and circuit which provides a relatively high conductive state of the transistor 173 when one of the inputs to the gate has a potential of approximately ground potential and the other input simultaneously has a potential or" minus 24 volts. Gne of these inputs 76a is connected to output line 6'3 oi the bistable 5o and the other input 7%[1 is connected to a line 175 extending from the common switch terminal 73 through the switch wiper or jumper 74 and terminal 76 to the asher bus 7S when the circuit is connected to provide a flashing indication for light 4. For a steady light indication, the line is connected to the minus 24 volt power bus 16 through switch wiper or jumper 74- and terminal di?. As will be explained, the flasher S1 provides a voltage on the flasher bus 78 which alternates between ground or zero potential and rninus 24 volts. Thus, when the circuit is adapted for flashing operation, and the bistable unit 65 is triggered into its conductive state, the transistor 173 of the and gate and power ampliiier 70 will be in a highly conductive state whenever the input line 175 is at minus 24 volts, the potential of the power bus le. During flashing operation, therefore, the conductive state of the transistor 173 alternates between a highly conductive and low conductive state to effect flashing of the alarm light 4 connected in the 'output of the transistor 173.

The base electrode 173e of transistor 173 is connected to the line 68 through a resistor 178, and is connected to the line 175 through a resistor 13@ and a rectifier 132 polarized to pass a negative voltage -to the base electrode 1735i. The base electrode 173e is also connected to a resistor connected to the negative power bus 16. The emitter electrode 1'73b is connected to the output line 71 joining with the grounded power bus 1S. The collector electrode 173e is connected through a resistor 157 to the negative power bus 16. The alarm light 4' is connected in parallel -with the last-mentioned resistor 187, and the dimming resistor 72 extends between the upper terminal or" the alarm light 4 and the grounded bus 18.

The transistor 173 being a type PNP transistor, the base electrode 173e rnust be at a positive potential with respect to the emitter electrode 173i) to provide a relatively non-conductive output state, and rnust be negative with respect to the emitter electrode 173!) to provide a relatively conductive output state. When the output line 58 or" the bistable unit en is substantially at the plus l2 volt potential of the power bus 118, which occurs during normal operation or" the variable involved, the potential of the input '76h is at ground or at minus 24 volts. The ratio of the net resistance between the base elect-rode 173m and the negative bus 1o relative to the net resistance between the base electrode and the ground bus 18 is such that this potential condition prevails when the bistable Iunit 66 is in its relatively non-conductive state. lt should be apparent that, when the input ila of the bistable unit 66 is at or near the ground potential of the bus 18, the potential at the base electrode 173m is negative to render the transistor highly conductive when the base electrode 173e is connected to minus 24 volts.

he alarm light i will thus be in ,a steady-on condition when the input line 175' is connected directly to the negative volt power bus 16 through terminal Sil* and will be flashing when connected to the flasher bus 7S.

Flasher Circuit 81 Reference should be made to FIG. 6b which shows -an exemplary circuit for the asher. The asher comprises a pair of type PNP transistors 18S and 191i. The transistor 138 has base, emitter and collector electrodes 188:1, 13S!) and 133C, respectively. The transistor 19t) has base, emitter and collector electrodes 1901.1, 19% and 190C, respectively. The emitter electrodes 18S!) and 119021 are connected to the grounded bus 18. The collector electrodes 188e and 196e are respectively connected through resistors 192 and 194 to the negative 24 volt bus 16. The base electrodes ISSa and 191m are respectively connested through resistors 196 and 198 to the negative 24 volt bus 16. Feedback branches are inserted between the transistors to eect a continuous flip-hop action. One of these feedback branches includes a capacitor 260 connected between the base electrode 188e of transistor 158 and the upper end of the resistor 194 associated with the collector electrode 19de of the transistor 198. The other feedback branch includes capacitor 202 connected between the base electrode 199:1 of transistor 196 and the upper end of resistor 192 associated with the collector electrode 188e of transistor 138.

As soon as one of the transistors 183 becomes highly conductive, the potential at the upper end of the resistor 192 suddenly rises from the potential of the negative volt 24power bus 16 to some potential positive with respect thereto. This sudden rise of potential is coupled through capacitor 202 to the base electrode 19h@ of transistor 19t) which mm'ntains this transistor in a relatively nonconductive state. As soon as the capacitor 232 becomes substantially fully charged, the relatively negative potential coupled to the base electrode 196m through resistor 193 is applied to the base electrode `19tla which starts the transistor 1% conduct-ing heavily. As soon as transistor 199 begins conducting heavily, the potential at the upper end of resistor 194 rises from the potential of the minus 24 volt bus 16 to a positive potential with respect thereto which potential is applied to the base electrode 1880. of transistor 188, which renders this transistor relatively non-conducting. As soon as the capacitor 200 becomes substantially fully charged, the transistor 188 begins to conduct heavily again, and this aforesaid process repeats itself providing a continuous flip-dop action between the resistors. Thus, the potenti-al at the upper end of; resistor 1% alternates between substantially ground potential and minus 24 volts, which variation of potential is applied through a resistor 2413- to the base electrode 205:1 of ya PNP control transistor 26S. The transistor 205 has an emitter electrode 2051 which is connected through a resistor 2%"7 to the plus l2 Volt bus 118. The juncture of the emitter electrode ZilSb and the resistor 297 is connected to the base electrode 211% of a PNP transistor 209. The transistor 26S has la collectorV Y :ground bus 118. The transistor 2619 has a collector electrode 269e which is connected directly to the negative 24 volt bus 16. A line 212 extends from the emitter electrode 20% of the transistor 20,9l to the tlasher bus 78. When lthe potential at the upper end of resistor 194 is substantially minus 24 volts, the base electrode 205a is negative with respect to the emitter electrode 2135b which is connected to the plus 12 bus 118 to thereby establish a high conductive state of the transistor 205. Conversely, when the voltage at the upper end of resistor i194 is substantially ground potential, the base electrode 20521 will be positive with respect to the emitter electrode 26517 and the transistor 26S will be substantially non-conductive. Whenever the transistor 2&5 conducts heavily, the potential at the base of the transistor 269 is substantially the potential of the minus 24 volt bus In?, thus ieiecting the high conductive state of the transistor 239-. Conduction of transistor 299 effectively `applies the potentiail of the minus 24 volt bus 16 on the line 212 leading to the flasher bus. When the transistor 295 is substantially non-conductive, the potential at the base electrode 20211 of transistor 209 is etectively the potential of the plus 12 volt power bus 118, which thereby renders the transistor 2%9 non-conductive. When the transistor 269 is non-conductive, the potential at the emitter electrode 289i) to which the ilasher bus line 212 is connected is substantially the ground potential of the bus 13.

H orlz Control Circuit rl'he horncontrol bistable unit 34 is substantially identical to the bistable unit 66 just described and corresponding components of these circuits have been similarly numbered, with a prime added to each number of the elements in bistable unit 34. Since the operation of these units is the same, a detailed explanation of the operation of the bistable unit 34 will not be given Suice it to say, when a negative pulse generated in the output of the pulse-forming network 30 -appears on the horn bus 32, the bistable unit 34 is set into its conductive state where the potential on the output line 68' is substantially ground potential. When the acknowledgement pushbutton switch S is momentarily closed, a negative voltage is vcoupled to the bistable unit through resistor 169' and rectifier 171' which resets the bistable unit into its normally non-conductive state. line 63 is substantially plus l2 volts.

The output line 68 of the bistable unit 34 feeds one of the inputs to an and gate and power amplifier 38 which is similar to the and gate andV power amplifier '70 previously described. Accordingly, the common components have been simil-arly numbered except that the reference numbers associated with the elements in circuit 38 have a prime aixed thereto. Since these two circuits operate in a similar manner, a detailed explanation of the operation of the and gate and power amplier will not be given. Suice it to say, when the line 68 feeding the input resistor 178 is substantially at ground potential, the transistor 17-3 is in its highly .conductive state which feeds energizing current to the input of the magnetic amplifier 40. The magnetic -ampliler 40' may comprise a rectangular hysteresis core 216 having a primary winding 218 and two secondary windings 220 and 222. The primary winding 218 is connected to the upper end of resistor 137 of the and gate and power amplifier 38. The other end of the primary winding 218 is connected to a resistor 224 leading the minus 24 volt bus 16. The upper end of the secondary winding 220 is connected through a rectifier 227 to 'a line 229 leading to the horn 6. The upper end of the lower secondary winding 222 is connected through -a rectier 231 leading to the line 229. The rectiers 227 and 231 are connected so as to provide full-wave rectiication. The 60 cycle voltage supply 42 is connected between the bottom end of the secondary winding 222 and the horn 6. As isV cornmon with magnetic amplifiers, when the input winding is supplied with a saturating current, the inductance of the secondary winding 22) and 222 is substantially reduced to zero so that a relatively high energizing current flows -in the horn 6. When, however, a relatively low current tlows in the primary winding 218, the transformer core is unsaturated and the induotance of the secondary windings 220 and 222 is so high that a negligible current ilows through the horn circuit. lt is thus apparent that when the bistable unit 34 is in a conductive state, the horn 6 will be sounded, and when the bistable unit 34 is in its non-conductive state, the horn 6 will be silent.

It should be understood that the present invention is not to be limited to the exemplary circuits shown and described in FIGS. 6a and 6b since numerous variations may be made therein without deviating from the various aspects of the invention illustrated in FIGS. 1-3 and 5.

Then, the voltage on output y What l claim as new and desire to protect by Letters Patent of the United States is:

il. Annunciator apparatus for monitoring the condition of a number of variables comprising rst and second visual lalarm means for each variable each operative from a normal indication to an alarm indication, audible alarm means, condition responsive means for each variable responsive to the condition of said variable to be monitored and having a normal indicating condition when the -variable to be monitored is normal and an abnormal indicating condition when the variable is abnormal, a first static element bistable control circuit for each variable exclusively for the associated first visual alarm means operated directly by said condition responsive means and connected between said condtion responsive means and said iirst visual alarm means, said control circuit operating the lassociated first visual alarm means to said normal and alarm indications when said condition responsive means is respectively in said normal and abnormal indicating conditions, a second static element bistable control circuit for each variable for the associated second visual alarm means independent of said first control circuit and connected between said condition responsive means and said second visual alarm means, said second control circuit effecting the operation of the associated second visual alarm means to its alarm indication when the condition of said condition responsive means changes from said normal indicating condition to said abnormalY indicating condition, a third static element bistable control circuit in common with said variable and `for said audible alarm means independent of said first and second control circuit and connected between said condition responsive means and said audible alarm means, said third control circuit effecting the operation of said .audible alarm means when the condition responsive means changes from said normal indicating condition to said abnormal indicating condition, the mutual independence of said rst, second and third control circuits providing operation of said means controlled by two of said control circuits despite the defective operation of one of the control circuits, and manually operable acknowledgement means for resetting said second and third control circuits to cancel said alarm indication on said second visual alarm means and to silence said audible alarm means.

2. Annunciator apparatus for monitoring a number of variables comprising: a source of energizing voltage having a pair of output terminals, a rst set of signal switch connecting terminal means associated with each'variable and adapted to be connected to a set of normally-open condition-responsive signal contacts, said iirst set of signal switch connecting terminals being connected in series with one of said voltage source terminals, a second set of signal switch connecting terminal means associated with each variable and adapted to be connected to a set of normally-closed condition-responsive signal contacts, said second set of signal switch connecting terminal means being connected in series with the other of said voltage source terminals, current-limiting resistor means connected in series between each second set of signal switch connecting terminal means and said one voltage source terminal, a visual alarm light for each variable, a control circuit for each visual alarm light including gate and power ampliiier means having an input adapted to provide a light-operating current in the output thereof when the input is connected to the potential of said one voltage source terminal, means connecting said visual alarm light to the output of said gate and power amplifier means, means connecting the input of said gate and power amplilier means selectively to the side of first set of signal switch connecting terminals remote `from said one voltage source terminal or to the side of said second set signal switch connecting terminals remote from the other voltage source terminal, wherein the visual alarm light is operated when a set of normally-open signal contacts connected across said first set of signal switch connecting terminal means close or when a set of normallyclosed signal contacts connected across said second set of signal switch connecting terminal means open.

3. Annunciator apparatus for monitoring a number of variables comprising: a source of energizing voltage having a pair of output terminals, a first set of signal switch connecting terminal means associated with each variable and adapted to be connected to a set of normally-open condition-responsive signal contacts, said iirst set of signal switch connecting terminals being connected in series with one of said voltage source terminals, a second set ci signal switch connecting terminal means associated with each variable and adapted to be connected to a set of normally-closed condition-responsive signal contacts, said second set of signal switch connecting terminal means being connected in series with the other of said voltage source terminals, current-limiting resistor means connected in series between each second set of signal switch connecting terminal means and said one voltage source terminal, a visual alarm light, a control circuit eX- clusively for said visual lalarm light including gate and power amplifier means having an input adapted to provide a light-operating current in the output thereof when the input is connected to the potential of said one voltage source terminal, means connecting said lvisual alarm light to the output of said gate and power amplifier mems, means connecting the input of said gate and power amplifier means selectively to the side of iirst set of signal switch connecting terminals remote from said one voltage source terminal or to the side of said second set signal switch connecting terminals remote from the other voltage source terminal, wherein the visual alarm light is operated when a set of normally-open signal contacts connected across said first set of signal switch connecting terminal means close or when a set of normallyclosed signal contacts connected across said second set of signal switch connecting terminal means open, audible alarm means, a control circuit for said audible alarm means comprising a bistable circuit in common with all of said variables and including two static control devices controlling the audible alarm means from the output of said bistable circuit, wherein the audible alarm means is energized only when the bistable circuit is in one of its conditions of operation, pulse-forming means associated with each variable, the output of said pulse-forming means being connected to trigger said bistable circuit and designed to produce a pulse which sets said bistable circuit to said one condition when the input of the pulseforming means is connected to the potential of said oneY voltage source terminal, and means for selectively connecting the input of said pulse-forming means to the side of said lirst set of signal switch connecting terminal means remote from' said one voltage source terminal when .a set ci? normally-open contacts is utilized and to the side of said second set of Vsignal switch connecting terminal means remote from the other voltage source terminal when a set of normally-closed signal contacts is utilized.

4. Annunciator apparatus -for monitoring ia number of variables comprising: a source of energizing voltage having a. pair of output terminals, a first set of signal switch connecting terminal means associated with each variable and adapted to be connected to la set of normally-open condition-responsive signal contacts, said first set of signal switch connecting terminals being connected in series with one of vsaid voltage source terminals, a second set of signal switch connecting terminal means associated with eachvariable and adapted to be connected to a set of normallly-closed condition-responsive signal contacts, said second set of signal switch connecting terminal means being connected in series with the Vother of said voltage source terminals,l current-'limiting resistor means connected in series between each second set oi signal switch connecting terminal means and said one voltage source terminal, a visual alarm lightl for each variable Vand having a pair of input terminals, one of which is connected to said other voltage source terminal, a control circuit for each visual alarm light including gate and power amplifier means having an input adapted to provide a light-operating current in the output 'thereof when the input is connected to the potential of said one voltage source terminal, and means selectively connecting the other input terminal of said visual alarm light directly to the side of said first set of signal switch connecting terminal means remote from said one voltage source terminal when a set of normally-open signal contacts is utilized, and to the output of said gate and power ampliiier means when a set of normally-closed signal contacts is utilized to be energized by said light-operating current thereof.

5. Annunciator apparatus for monitoring a number of variables comprising: a source of energizing voltage having a pair of output terminals, a first set of signal switch connecting terminal means associated with each variable and adapted to be connected to a set of normally-open condition-responsive signal contacts, said first set of signal switch connecting terminals being connected in series with one of said voltage source terminals, a second set of signal switch connecting terminal means associated with each variable and adapted to be connected to a se-t of normally-closed condition-responsive signal contacts, said second set of signal switch connecting terminal means being connected in series with other of said voltage source terminals, current-limiting resistor means connected in series between each second set of sigial switch connecting terminal means and said one voltage source terminal, a visual alarm light having a pair of input terminals, one of which is connected to said other voltage source terminal, a control circuit exclusively for said visual alarm light including gate and power amplifier means having an input adapted to provide a lightoperating current in the output thereof when the input is connected to the potential of said one voltage source terminal, and means selectively connecting the other input terminal of said visual alarm light directly to the side of said iirst set of signal switch connecting 'terminal means remote from said one voltage source terminal when a set of normally-open signal contacts is utilized,

'and to the output of said gate and power amplifier means when a set of'normally-closed signal contacts is utilized to be energized by said light-operating current thereof, audible alarm means, a control circuit :for said audible alarm means comprising a bistable circuit including two static control devices controllingthe audible alarm means Yfrom the output ot said bistable circuit, wherein the auble alarm means is energized only when the bistable circuit is in one of its conditions of operation, pulseforming means whose output is connected to trigger said bistable circuit and which is adapted to produce a pulse which sets said bistable circuit to said one condition when the input oi the pulse-forming means is connected to the potential of said one voltage source terminal, and means for selectively connecting the input of said pulse-forming means to the side of said first set of signal switch connecting terminal means remote from said one voltage source terminal when a set of normally-open contacts is utilized and to the side of said second set of signal switch Y connecting terminal means remote from the other voltage source terminal when a set of normally-closed signal contacts is utilized.

6. Annunicator apparatus comprising a source of direct current energizing voltage having relative positive and negative terminals, la irst visual alarm light connected to one of said voltage source terminal-s, condition-responsive signal contacts which have one position when an associated variable to be monitored is normal and another position when the variable to be monitored is abnormal, a control circuit exclusively for said first visual alarm light, said latter control circuit comprising :gate and power amplifier means having an input providing a light-operating current in the output thereof when a gate-opening potential is connected to the input of said gate and power amplifier means, a transistor bistable circuit having an output coupled to said input and which provides a gate-opening potential at its output only when the bistable circuit is in one of its conditions of operation, and pulse-forming means having an output which operates the bistable circuit to said one condition when the input to said pulse-forming circuit is connected :to the potential of one of said voltage source terminals, means connecting said lirst visual alarm light to the output of said :gate and power amplifier means, an audible alarm means, a control circuit for said audible alarm means and operating independently of the control circuit of said visual alarm light, `wherein defective operation of one of the control circuits will not effect the operation of the other, the control circuit of said audible alarm means comprising gate and power amplier means having an output providing a current for energizing said audible alarm means when a gate-opening potential is connected vto the input thereof, a transistor bistable circuit having an output connected to the later input and at which is produced a `gate-opening potential only when the bistable circuit is in `one of its conditions of operation, and pulsefonming means connected to trigger said bistable circuit Iand 'which provides a pulse output which operates said bistable circuit to said one condition when the input thereof is coupled to the potential of one of said voltage source terminals, means connecting the condition-responsive signal contacts to the inputs of both of said pulse-forming means wherein the inputs thereof are coupled to thepotential of one of said voltage source terminal when said signal contacts are in their position indicating an abnormal variable, manually operable switch means, and circuit means connecting said manually operable switch means to Vthe said bistable circuits for resetting the same to cancel the gate-opening potentials in their outputs to silence the audible alarm means and to change the visual indication of said visual alarm light.

References Cited in the file of this patent UNITED STATES PATENTS 2,154,065 Davis et al Apr.'11, 1939 2,600,132 Seaton June 10, 1952 2,709,250 M-armorstone May 24, 1955 2,730,704 Warren Ian. 10, 1956 2,832,068 Warren Apr. 22, 1958 2,832,948 Derr etal Apr. 29, 1958 2,913,044 Mobley Nov. 17, 1959 2,931,018 Tellefsen et a1 Mar. 29, 1960 3.029.421 Beguin ,;l Apr. y10, 1962 

1. ANNUNCIATOR APPARATUS FOR MONITORING THE CONDITION OF A NUMBER OF VARIABLES COMPRISING FIRST AND SECOND VISUAL ALARM MEANS FOR EACH VARIABLE EACH OPERATIVE FROM A NORMAL INDICATION TO AN ALARM INDICATION, AUDIBLE ALARM MEANS, CONDITION RESPONSIVE MEANS FOR EACH VARIABLE RESPONSIVE TO THE CONDITION OF SAID VARIABLE TO BE MONITORED AND HAVING A NORMAL INDICATING CONDITION WHEN THE VARIABLE TO BE MONITORED IS NORMAL AND AN ABNORMAL INDICATING CONDITION WHEN THE VARIABLE IS ABNORMAL, A FIRST STATIC ELEMENT BISTABLE CONTROL CIRCUIT FOR EACH VARIABLE EXCLUSIVELY FOR THE ASSOCIATED FIRST VISUAL ALARM MEANS OPERATED DIRECTLY BY SAID CONDITION RESPONSIVE MEANS AND CONNECTED BETWEEN SAID CONDITION RESPONSIVE MEANS AND SAID FIRST VISUAL ALARM MEANS, SAID CONTROL CIRCUIT OPERATING THE ASSOCIATED FIRST VISUAL ALARM MEANS TO SAID NORMAL AND ALARM INDICATIONS WHEN SAID CONDITION RESPONSIVE MEANS IS RESPECTIVELY IN SAID NORMAL AND ABNORMAL INDICATING CONDITIONS, A SECOND STATIC ELEMENT BISTABLE CONTROL CIRCUIT FOR EACH VARIABLE FOR THE ASSOCIATED SECOND VISUAL ALARM MEANS INDEPENDENT OF SAID FIRST CONTROL CIRCUIT AND CONNECTED BETWEEN SAID CONDITION RESPONSIVE MEANS AND SAID SECOND VISUAL ALARM MEANS, SAID SECOND CONTROL CIRCUIT EFFECTING THE OPERATION OF THE ASSOCIATED SECOND VISUAL ALARM MEANS TO ITS ALARM INDICATION WHEN THE CONDITION OF SAID CONDITION RESPONSIVE MEANS CHANGES FROM SAID NORMAL INDICATING CONDITION TO SAID ABNORMAL INDICATING CONDITION, A THIRD STATIC ELEMENT BISTABLE CONTROL CIRCUIT IN COMMON WITH SAID VARIABLE AND FOR SAID AUDIBLE ALARM MEANS INDEPENDENT OF SAID FIRST AND SECOND CONTROL CIRCUIT AND CONNECTED BETEWEEN SAID CONDITION RESPONSIVE MEANS AND SAID AUDIBLE ALARM MEANS, SAID THIRD CONTROL CIRCUIT EFFECTING THE OPERATION OF SAID AUDIBLE ALARM MEANS WHEN THE CONDITION RESPONSIVE MEANS CHANGES FROM SAID NORMAL INDICATING CONDITION TO SAID ABNORMAL INDICATING CONDITION, THE MUTUAL INDEPENDENCE OF SAID FIRST, SECOND AND THIRD CONTROL CIRCUITS PROVIDING OPERATION OF SAID MEANS CONTROLLED BY TWO OF SAID CONTROL CIRCUITS DESPITE THE DEFECTIVE OPERATION OF ONE OF THE CONTROL CIRCUITS, AND MANUALLY OPERABLE ACKNOWLEDGEMENT MEANS FOR RESETTING SAID SECOND AND THIRD CONTROL CIRCUITS TO CANCEL SAID ALARM INDICATION ON SAID SECOND VISUAL ALARM MEANS AND TO SILENCE SAID AUDIBLE ALARM MEANS. 